This invention relates to a thermal isolation plate for a probe card.
A semiconductor tester may be used in conjunction with other equipment for testing semiconductor integrated circuit (IC) devices at various stages of manufacture.
A known form of semiconductor tester includes a test head provided with a docking plate. Pin cards are mounted in the test head and pogo pins attached to the pin cards project through the docking plate. In use of the tester, a load board (otherwise known as a DUT board) specific to the type of device to be tested is positioned relative to the docking plate so that the pogo pins of the pin cards engage contact pads on the load board. At the opposite face, the load board is provided with contact elements for electrically interfacing to the device under test (DUT).
A semiconductor tester of this kind may be used in conjunction with a wafer prober for testing devices in the wafer stage, i.e. before dicing and packaging.
One form of wafer prober includes a horizontal prober head stage formed with an aperture, a receptacle for receiving a cassette containing multiple wafers, a chuck positioned below the prober head stage for receiving a wafer, a translation mechanism for translating the chuck between a loading location adjacent the cassette receptacle and a probing location in which the chuck is beneath the aperture in the prober head stage, and a robot for transferring wafers between the cassette and the chuck.
A ring insert is fitted in the aperture in the prober head stage and is attached to the head stage. A load board, which is frequently referred to as a probe card in the context of a wafer prober, is fitted in the ring insert. The probe card may be locked at its periphery to the interior of the ring insert. The contact elements of the probe card are probe needles which project downwardly from the probe card. The ring insert has docking structures for engaging the docking plate of the test head. The test head is positioned above the ring insert and is docked thereto and the pogo pins engage the contact pads at the upper surface of the probe card. By repeatedly raising the chuck so that the probe needles engage the contact pads of an individual die, lowering the chuck, displacing the chuck to position a different die beneath the probe needles and raising the chuck, the different devices embodied in the wafer can be presented sequentially to the probe needles for testing.
When this type of wafer prober is used to test wafers embodying a different type of integrated circuit device, the test head is undocked from the ring insert, the probe card is removed from the ring insert and a new probe card, specific to the new type of IC device, is installed in the ring insert.
Another type of wafer prober employs a bottom probe card changer, which avoids the need to undock the test head from the ring insert in order to change the probe card. In a prober having a bottom probe card changer, the probe card is mounted in a frame or tray which is releasably locked to the underside of the prober head stage. When it is necessary to change the probe card, the chuck is moved to a non-interfering position and the tray is released from the prober head stage and is moved within the wafer prober housing to an access port. The tray, including the probe card, may be removed from the prober via the access port and replaced with a substitute tray, containing the appropriate probe card, or the probe card can be removed from the tray and replaced with the appropriate probe card. In either event, the tray is then automatically withdrawn into the prober, placed beneath the ring insert and locked to the prober head stage.
It has hitherto been conventional to test integrated circuits at normal room temperature, typically about 18.degree. C. However, since some integrated circuit devices operate at substantially higher temperatures (even temperatures well above 100.degree. C.), it has been recognized that it may be desirable to test these devices at an elevated temperature. For this purpose, the chuck of the prober may include a heater for heating the wafer held by the chuck so that the test will provide a realistic indication of the behavior of the devices embodied in the wafer at an elevated temperature.
In the conventional wafer prober provided with a heated chuck, heat may be transferred from the chuck to the probe card by radiation, conduction and/or convection, elevating the temperature of the probe card. Thermally induced strain may distort the probe card to such an extent that the probe needles do not reliably engage the respective connection pads of the device under test. Consequently, the accuracy of test results is compromised. Further, the distortion of the probe card does not remain constant with time, such that it can be accommodated simply by a one-time adjustment in the position of the chuck, because as the chuck is translated to present successive devices to the probe needles, different regions of the probe card are heated and undergo thermally induced strain.
Semiconductor IC devices frequently have several hundred contact pads. This generally necessitates that a like number of pogo pins engage the probe card. Each pogo pin includes a spring, which is compressed when the test head is docked to the ring insert. The spring force exerted by a single pogo pin on the probe card is quite small, but the total force exerted by several hundred pins may be sufficient to cause undesirable flexing of the probe card.
In order to minimize flexing of the probe card, it is known to mount a steel stiffener plate in the ring insert beneath the probe card. The stiffener plate is annular and is secured at its periphery to the ring insert. The probe card is placed on top of the stiffener plate and is locked at its periphery to the interior of the ring insert. The probe needles project downward through the central aperture of the stiffener plate.